For example, if you wanted to paint your room, you would go buy the paint, brushes, plastic drop cloths to protect your furniture, painters tape and maybe even some paper to mask off the things you want to keep unpainted. At the end of the project, you tear off all the tape and paper, and ball up the plastic drop cloths and dump them in the garbage. Why??? You spent good money on that stuff, they should be part of the room now, shouldn't they? Of course not, you view those expendable materials as necessary costs required to help you complete the project. You never had any intention of incorporating them into the finished project. They were just to facilitate a good job.